Comparison of Frequency-Specific Transcranial Alternating Current Stimulations on Cognitive Function in Patients With Mild Cognitive Impairment

Objective This study aimed to compare the effects of theta and gamma transcranial alternating current stimulation (tACS) on cognitive function and memory in individuals with mild cognitive impairment (MCI). Methods The participants were assigned to one of three conditions: sham, theta (5 Hz), or gamma (40 Hz) tACS, targeting the dorsolateral prefrontal cortex (DLPFC) for approximately 30 min. Cognitive tasks were conducted before and after stimulation, including the Digit Span and Trail Making Test A (TMT-A). Results The results indicated significant improvements in the gamma tACS group, specifically a reduction in TMT-A errors. In contrast, no significant effects were observed in the sham or theta groups. Conclusion These findings suggest that gamma tACS enhances working memory, processing speed, and cognitive flexibility, potentially due to its modulating neural activity within the DLPFC and restoring effective theta-gamma coupling. Conversely, theta tACS did not yield improvements, likely because of the elevated baseline theta levels and disrupted oscillatory dynamics observed in patients with MCI. This study underscores the potential of gamma tACS as a promising intervention for cognitive decline in MCI and further suggests the necessity of a comprehensive approach that considers the electrophysiological abnormalities and dynamic oscillatory patterns in MCI.